Cepheus

by Tammy Plotner on October 24, 2008

Cepheus

Cepheus

Cepheus is one of the 48 original constellations listed by Ptolemy and the king of the north remains as one of the 88 modern constellation recognized by the International Astronomical Union. Bordered by Cygnus, Lacerta and Cassiopeia, it contains only one bright star, but seven major stars and 43 which have Bayer/Flamsteed designations. Cepheus is a circumpolar constellation of the northern hemisphere and is easily seen at visible at latitudes between +90° and ?10° and best seen during culmination during the month of November.

In mythology, Cepheus represents the mythical king of Aethiopia – and husband to the vain queen Cassiopeia. This also makes him the father of the lovely Andromeda and a member of the entire sky saga which involves jealous gods and mortal boasts. Perhaps his part in the whole drama is why his crown only appears to be seen in the fainter stars when he’s upside down?

For the unaided eye observer, start first with Cepheus’ brightest star – Alpha. It’s name is Alderamin and it’s going through stellar evolution – moving off the main sequence into a subgiant, and on its way to becoming a red giant as its hydrogen supply depletes. What’s very cool is Alderamin is located near the precessional path traced across the celestial sphere by the Earth’s north pole. That means that periodically this star comes within 3° of being a pole star!

Keeping that in mind, head off for Gamma Cephei. Guess what? Due to the precession of the equinoxes, Errai will become our northern pole star around 3000 AD and will make its closest approach around 4000 AD. (Don’t wait up, though… It will be late.) However, you can stay up late enough with a telescope or binoculars to have a closer look at Errai, because its an orange subgiant binary star that’s also about to go off the main sequence and its accompanied by a red dwarf star. What’s so special about that? Well, maybe because a planet has been discovered floating around there, too!

Now let’s have some fun with a Cepheid variable star that changes enough in about 5 days to make watching it fun! You’ll find Delta on the map as the figure 8 symbol and in the sky you’ll find it 891 light-years away. Delta Cephei is binary star system and the prototype of the Cepheid variable stars – the closest of its type to the Sun. This star pulses, just like your heart, and every 5.36634 days its stellar magnitude varies from 3.6 to 4.3. But that’s not all… Its spectral type varies, too – going from F5 to G3. Try watching it over a period of several nights. Its rise to brightness is much faster than its decline! Oh… And take a peek in a telescope. There is a companion star, separated from Delta Cephei by 41 arc seconds.

Are you ready to examine two red supergiant stars? If you live in a dark sky area, you can see these unaided, but they are much nicer in binoculars. The first is Mu Cephei, marked by the U shape on our chart. It’s called Herschel’s Garnet Star for a very good reason… It is beautiful. In his 1783 notes, Sir William Herschel wrote: “a very fine deep garnet colour, such as the periodical star ? ceti” and the name stuck when Giuseppe Piazzi included the description in his catalog! Now compare it to VV Cephi, right smack in the middle of the map. VV is absolutely a supergiant star, and it is of the largest stars known. In fact, VV Cephei is believed to be the third largest star in the entire Milky Way Galaxy! VV Cephei is 275,000-575,000 times more luminous than the Sun and is approximately 1,600–1,900 times the Sun’s diameter. If placed in our solar system, the binary system would extend past the orbit of Jupiter and approach that of Saturn. Some 3,000 light years awat from Earth, matter continuously flows off this bad boy and into its blue companion… Stellar wind flows off the system at a velocity of approximately 25 kilometers per second… And some body’s Roche lobe gets filled!

For some rich field telescope and binocular fun from a dark sky site, try your luck with IC1396. This 3 degree field of nebulosity can even be seen unaided at times! Inside you’ll find an open star cluster (hence the designation) and photographically the whole area is criss-crossed with dark nebulae.

For a telescope challenge, see if you can locate both Spiral galaxy NGC 6946 and galactic cluster NGC 6939 about 2 degrees southwest of Eta Cepheus. NGC 6946 is sometimes called the Fireworks Galaxy for its supernovae rate and high volume of star formation. About 40 arc minutes northwest of NGC 6946 – is about 8th magnitude, well compressed and contains about 80 stars.

More? Then try NGC 7023 – The Iris Nebula. NGC 7023 was first discovered by Sir William Herschel on October 18, 1794 and since that time it has had a rather confusing catalog history. As usual, Herschel’s notes made the correct assumption of “A star of 7th magnitude. Affected with nebulosity which more than fills the field. It seems to extend to at least a degree all around: (fainter) stars such as 9th or 10th magnitude, of which there are many, are perfectly free from this appearance.” So where did the confusion come in? It happened in 1931 when Per Collinder decided to list the stars around it as a star cluster Collinder 429. Then along came Mr. van den Berg, and the little nebula became known as van den Berg 139. Then the whole group became known as Caldwell 4! So what’s right and what isn’t? According to Brent Archinal, “I was surprised to find NGC 7023 listed in my catalog as a star cluster. I assumed immediately the Caldwell Catalog was in error, but further checking showed I was wrong! The Caldwell Catalog may be the only modern catalog to get the type correctly!” This faint nebula can be achieved in dark skies with a 114-150mm telescope, but larger aperture will help reveal more subtle details since it has a lower surface brightness. Take the time at lower power to reveal the dark dust “lacuna” around it reported so many years ago, and to enjoy the true beauty of this Caldwell gem.

Still more? Then head off with your telescope for IC1470 – but take your CCD camera. IC1470 is a compact H II region excited by a single O7 star associated with an extensive molecular cloud in the Perseus arm!

Source: Chandra Observatory
Constellation Chart Provided by Your Sky.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

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